Dependence of the viscosity of nanofluids on nanoparticle size and material

A thermodynamic model of nanofluid viscosity based on a generalized Maxwell-type constitutive equation

“…Our results are also shown to be in good accord with these obtained by Rudyak and Krasnolutskii [42] using a molecular dynamics method. It is seen that for volume fractions higher than 0.06, the agreement between the model and the data from [42] is less satisfactory, which can be understood by recalling that Einstein's model is only valid for small volume fractions.…”

“…This example has been chosen in order to compare with a recent analysis by Rudyak and Krasnotlutskii [42] and to provide an answer to the controversial question of increase or decrease of nanofluid viscosity with the particle size. The nanoparticles are assumed to be rigid spheres uniformly dispersed in the fluid carrier, the temperature is fixed at T= 300 K and volume fraction of particles is small, ranging from 0.01 to 0.10.…”

“…The mean free path is found to be given by = 3/2 − 1 ≈ 0.043 nm, after taking for the Van der Waals radius, = 0.19 nm. The value of lAr-Ar takes into account the radius of an interstitial sphere that would fit between closely packed spheres of Ar without distorting the structure explicitly: this particular value has been selected because of the strong packing of the Ar molecules considered in [42] to which our results will be compared. Since no value for the thickness h of the boundary layer surrounding Li particles in…”

“…The results are compared with experimental data and with Einstein's model [11], which accounts only for the volume fraction of dispersed particles. Data from [42] result may be interpreted by the fact that by increasing the volume fraction, one increases the interfacial surface between particles and fluid giving rise to a larger resistance to deformation, whence a higher viscosity. Our results are also shown to be in good accord with these obtained by Rudyak and Krasnolutskii [42] using a molecular dynamics method.…”

“…Data from [42] result may be interpreted by the fact that by increasing the volume fraction, one increases the interfacial surface between particles and fluid giving rise to a larger resistance to deformation, whence a higher viscosity. Our results are also shown to be in good accord with these obtained by Rudyak and Krasnolutskii [42] using a molecular dynamics method. It is seen that for volume fractions higher than 0.06, the agreement between the model and the data from [42] is less satisfactory, which can be understood by recalling that Einstein's model is only valid for small volume fractions.…”